The present invention relates to a corrective network and, more particularly, to an equalization circuit arrangement which is employed in transmission systems to obtain a desired overall frequency response.
It is generally known in the prior art to provide corrective networks for improving the frequency-response characteristics of a transmission system. These corrective networks have adjustable components which either increase or decrease the response of a transmission system at a desired frequency or band of frequencies across the overall frequency spectrum. The adjustable components are operative to generate resonances having peak and valleys so as to set the amplitude (gain or loss) and/or the width of the resonances and/or the center frequency at which the resonance occurs. By using any or all of the parameters, it is possible to either boost or suppress respective portions of the frequency-response characteristic.
As noted in German Pat. Nos. 828,258 and 828,718, as well as published German patent application Nos. 1,261,553 and 1,267,261, the prior art corrective networks all share the common disadvantage that they employ a plurality of discrete switching circuits or a potentiometer. The use of multi-stage switching and/or potentiometers, however, has caused many difficulties because switching contact must be repeatedly made.
In an attempt to obviate these aforementioned difficulties, it is also known to provide a device effective for generating a plurality of resonant-like peaks and valleys across the frequency spectrum. However, this prior-art device is possessed of many drawbacks. First of all, this device has a rather large attenuation. Secondly, the signal source must have a very small internal impedance in order that the loading produces no undesirable frequency response. Finally, active amplifying stages are required to be connected to the device in order to offset the rather high loss presented by the device.